<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script src="./lib/vue.js"></script>
</head>
<body>
    <div id="app">
        <input type="text" v-model="firstname">+
        <input type="text" v-model="lastname">=
        <input type="text" v-model="fullname">
    </div>
    <script>
        var vm = new Vue({
            el: '#app',
            data: {
                firstname: '',
                lastname: '',
                fullname: ''
            },
            methods: {},
            watch: {//使用这个属性可以监视data中指定数据的变化，触发watch中对应的function处理函数
                firstname: function(newVal){
                    //this.fullname = this.firstname + '-' + this.lastname
                    this.fullname = newVal + '-' + this.lastname
                },
                lastname: function(newVal){
                    this.fullname = this.firstname + '-' +newVal
                }
            }
        });
    </script>
</body>
</html>